Method for producing vinyl polymer

ABSTRACT

A method for producing a vinyl polymer including a polymerization step of using a composition including a microcapsule and polymerizing a vinyl monomer by radical reaction to produce a vinyl polymer, in which the microcapsule has a core/shell structure, and the shell includes a water-soluble polymer and the core includes an organic peroxide. The water-soluble polymer is preferably at least one water-soluble polymer selected from the group consisting of polyvinyl alcohol, cellulose derivatives, gelatin, poly(meth)acrylic acid derivatives, polyvinylpyrrolidone, and polyethylene oxide.

CROSS-REFERENCE TO RELATED APPLICATION(S)

The present application claims priority to and incorporates by referencethe entire contents of Japanese Patent Application No. 2019-037345 filedin Japan on Mar. 1, 2019.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a method for producing a vinyl polymer.

2. Description of the Related Art

Conventionally, an organic peroxide has been known as a polymerizationinitiator of a vinyl monomer (for example, a vinyl chloride monomer) byradical reaction. The organic peroxide diluted with an organic solventor emulsified with water has an easy handling and excellent safety andthus is put into practical use.

In general, the polymerization of the vinyl chloride monomer or thepolymerization of the vinyl chloride monomer and a monomer that can becopolymerized with the vinyl chloride monomer is carried out by abatch-wise suspension polymerization method. More specifically, thebatch-wise suspension polymerization method is a method for charging anaqueous medium, the monomer, and a dispersion agent (suspension agent)into a polymerization reactor, subsequently charging the polymerizationinitiator in the form described above, and subsequently raising atemperature inside the polymerization reactor to a predeterminedpolymerization reaction temperature by flowing hot water through ajacket to carry out the polymerization reaction.

In recent years, in the production of a vinyl chloride polymer, a largerpolymerization reactor has been formed and a reaction time has beenshortened for the purpose of an increase in productivity. As one of themethods for shortening the reaction time, a method for raising apolymerization rate by increasing the amount of the polymerizationinitiator to be charged is exemplified. However, as the amount of thepolymerization initiator is increased in the polymerization reactorhaving a larger size, it takes time for the polymerization initiator tobe uniformly dispersed in the polymerization reactor. Consequently, thenonuniform concentration distribution of the polymerization initiator isgenerated. This causes the problem of partially generating particleshaving less internal pore called glassy particles and increasing thenumber of fish eyes.

As another method for shortening the polymerization time, a method forpreviously charging the vinyl chloride monomer, and subsequentlycontinuously charging warm water to shorten the temperature rising timeand increase the productivity is exemplified. This method allows theinternal temperature at the time of the completion of warm water chargeto be adjusted to some extent by the temperature of the warm water to becharged. As described above, the temperature rising time can besubstantially shortened by adjusting the internal temperature at thetime of the completion of the charge to approximately the predeterminedpolymerization temperature (in the present specification, this method isalso called a high temperature water-charged polymerization method).However, this method has higher temperature inside the polymerizationreactor at the time of charging the polymerization initiator than thatof the conventional method and thus the polymerization reaction israpidly promoted in the vicinity of the place where the polymerizationinitiator is charged. As a result, the problem of more easily generatingthe non-uniformity of the concentration distribution of thepolymerization initiator and thus increasing the number of fish eyes hasarisen.

The vinyl chloride polymer is a useful resin that is inexpensive and hasexcellent physical properties and is used for a wide range ofapplications such as a soft product field and a hard product field.Examples of the applications include a coated electric wire, a lap film,and a sheet in the soft product field. The surface of the products suchas the lap film and the sheet should be smooth and, in particular, thegeneration of the fish eyes should be avoided. With respect to theparticles forming the fish eyes, foreign matters except the resin suchas contamination and a resin generated by partially heating in highintensity at the drying process in the production process of the vinylchloride polymer are some of the causes. On the other hand, notdissolving such fish eyes but making the vinyl chloride polymerparticles themselves generated in the polymerization reactor bedifficult to form fish eyes has also been tried.

Specifically, it has been well known that the production of the vinylchloride polymer having an excellent plasticizer absorption propertyresults in reduction in fish eyes. Many methods for producing the vinylchloride polymer having an excellent plasticizer absorption propertyhave been reported. For example, Japanese Patent Application Laid-openNo. H8-3206 has described simultaneous use of (1) partially saponifiedpolyvinyl alcohol having an average degree of polymerization of 150 to600 and a degree of saponification of 20% by mole to 55% by mole and (2)hydroxypropyl methylcellulose having a methoxy group content of 19% byweight to 30% by weight, a hydroxypropoxy group content of 4% by weightto 15% by weight, and a viscosity of a 2% by weight aqueous solution ofthe hydroxypropyl methylcellulose at 20° C. of 100 cps or more in aspecific weight ratio. Specifically, Japanese Patent ApplicationLaid-open No. H8-3206 has described that (1) and (2) are simultaneouslyused in a weight ratio of (1)/(2) of 2/1 to 5/1. As described above, amethod for producing the porous vinyl chloride polymer having theexcellent plasticizer absorption property by the suspensionpolymerization method has been developed. However, use of a large amountof polyvinyl alcohol having the small degree of saponification in theinitial stage of the polymerization causes a risk in which capability ofprotecting the surface of the oil droplet of the vinyl chloride monomerimmediately after the start of the polymerization may be rapidlydeteriorated and thus the obtained polymer can form coarse particles. Anincrease in the amount of the dispersion agent to be used in order toprevent the coarse particle formation avoids generating the problem offorming the coarse particles. However, the surface of the oil droplet ofthe vinyl chloride monomer is covered with the thick film of thedispersion agent. As a result, the polymerization initiator taken in theoil droplet of the vinyl chloride monomer is difficult to aggregate withanother oil droplet of the vinyl chloride monomer and difficult todisperse and thus non-uniformity of the concentration distribution ofthe polymerization initiator is generated to increase the fish eyes.

Japanese Patent No. 4688991 has described the use of 0.04 part by massto 0.08 part by mass of partially saponified polyvinyl alcohol (A)having an average degree of polymerization of 2,000 to 3,000 and adegree of saponification of 75% by mole to 85% by mole relative to 100parts by mass of the vinyl chloride monomer and 0.01 part by mass to 0.1part by mass of partially saponified polyvinyl alcohol (B) having anaverage degree of polymerization of 100 to 700 and a degree ofsaponification of 20% by mole to 55% by mole relative to 100 parts bymass of the vinyl chloride monomer. Japanese Patent No. 4688991 has alsodescribed that 10% to 80% out of the total amount to be used of thepartially saponified polyvinyl alcohol (A) is charged before the startof the polymerization and the remaining partially saponified polyvinylalcohol (A) is added to the polymerization system at the time ofreaching the polymerization conversion ratio to 1% to 10%. This allowsthe porous vinyl chloride polymer having the excellent plasticizerabsorption property to be obtained. However, a risk of destabilizing thepolymerization system depending on the amount of the suspension agent tobe added during the polymerization or the timing of the addition andthus forming coarse particles of the obtained polymer may arise.

It can be said that the features of these conventional techniques arebased on the devisal of the dispersion agent to be used in theproduction of the vinyl chloride polymer polymerized by the suspensionpolymerization. This is because the inside of the obtained vinylchloride resin is possibly highly porous by devising the degree of thesurface activation capacity of the dispersion agent to be used. It isnot difficult to imagine that the high porous resin has a structure ofeasily absorbing a plasticizer into deeper inside. The resin having sucha structure of easily absorbing a plasticizer into deeper inside may beeasy to be entirely plasticized. Consequently, the resin is easy to bemelted at the time of kneading and thus generation of the fish eyes isreduced.

However, such conventional techniques are not necessarily advantageousfrom the viewpoint of carrying out polymerization stably. This isbecause the action of avoiding agglomeration of the monomer oil dropletswith each other in the suspension polymerization of the vinyl chloridepolymer is possibly insufficient by using a dispersion agent havingextremely high surface activation capacity or decreasing the amount ofthe dispersion agent added at the initial stage of the polymerization.The devisal of the dispersion agent to be used in the polymerization mayresult in providing a special product in which the basic properties ofthe obtained vinyl chloride polymer such as an average particlediameter, an amount of a plasticizer to be absorbed, and an apparentdensity are changed. Therefore, the conventional techniques are by nomeans desired from the viewpoint of production control.

As described above, the production methods described in Japanese PatentApplication Laid-open No. H8-3206 and Japanese Patent No. 4688991 haveproblems of destabilization of the polymerization and change in thebasic properties of the produced vinyl chloride polymer. Vinyl polymersother than the vinyl chloride polymer also have the same problems.

SUMMARY OF THE INVENTION

In view of the aforementioned, an object of the present invention is toprovide a method for producing a vinyl polymer that does not involve theproblems of the destabilization of the polymerization or the change inthe basic properties of the produced vinyl polymer and can reduce fisheyes in the produced vinyl polymer.

A method for producing a vinyl polymer according to one aspect of thepresent invention includes a polymerization step of using a compositionthat includes a microcapsule and polymerizing a vinyl monomer by radicalreaction to produce a vinyl polymer, wherein the microcapsule has acore/shell structure, and the shell includes a water-soluble polymer andthe core includes an organic peroxide.

According to another aspect of the present invention, in the method forproducing the vinyl polymer, it is preferable that the water-solublepolymer is at least one water-soluble polymer selected from the groupconsisting of polyvinyl alcohol, cellulose derivatives, gelatin,poly(meth)acrylic acid derivatives, polyvinylpyrrolidone, andpolyethylene oxide.

According to still another aspect of the present invention, in themethod for producing the vinyl polymer, it is preferable that thepolyvinyl alcohol is partially saponified polyvinyl alcohol having adegree of saponification of 80% by mole or more and 99.5% by mole orless and an average degree of polymerization of 1,500 or more and 3,500or less.

According to still another aspect of the present invention, in themethod for producing the vinyl polymer, it is preferable that themicrocapsule has a median diameter (D50) of 15 μm or less.

According to still another aspect of the present invention, in themethod for producing the vinyl polymer, it is preferable that theorganic peroxide has a 10-hour half-life temperature in benzene at aconcentration of 0.1 mol/L of 70° C. or less.

According to still another aspect of the present invention, in themethod for producing the vinyl polymer, it is preferable that thepolymerization step is a step of polymerizing vinyl chloride as thevinyl monomer to produce a vinyl chloride polymer as the vinyl polymer.

The above and other objects, features, advantages and technical andindustrial significance of this invention will be better understood byreading the following detailed description of presently preferredembodiments of the invention, when considered in connection with theaccompanying drawings.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the embodiment will be described in detail. It should benoted that the present invention is not limited at all by the followingembodiment.

The method for producing the vinyl polymer according to the embodimentincludes a polymerization step of using the composition including themicrocapsule and polymerizing the vinyl monomer by the radical reactionto produce the vinyl polymer, in which the microcapsule has thecore/shell structure, and the shell includes the water-soluble polymerand the core includes the organic peroxide.

At the time of the production of the vinyl polymer, use of themicrocapsule allows the concentration distribution of the organicperoxide having a role as the polymerization initiator to be uniform inthe polymerization reactor. This allows the fish eyes in the producedvinyl polymer to be reduced.

As described above, use of the method for producing the vinyl polymeraccording to the embodiment allows the reduction in the fish eyes in thevinyl polymer to be achieved without devising the dispersion agent. Inother words, use of the method for producing the vinyl polymer accordingto the embodiment allows the reduction in the fish eyes in the vinylpolymer to be achieved without concerns about the coarse particleformation associated with the reduction in polymerization stability and,in addition, without concerns about the change in the basic propertiesin the vinyl polymer.

As described above, with regard to the particles forming the fish eyes,foreign matters except the resin such as contamination and a resingenerated by partially heating in high intensity at the drying processin the production process of the vinyl chloride polymer are some of thecauses. However, the present embodiment does not aim to solve such fisheyes but aims to make the vinyl chloride polymer particles themselvesgenerated due to nonuniformity of the concentration distribution of thepolymerization initiator in the polymerization reactor be difficult toform the fish eye. Use of the microcapsule allows this object to beachieved. The embodiment also has a feature of easily removing theremaining monomer in the vinyl polymer and providing a scale preventioneffect.

Hereinafter, the method for producing the vinyl polymer according to theembodiment will be described more specifically. Examples of the vinylmonomer used in the production method include monomers such as vinylchloride, styrene, (meth)acrylic acid esters, (meth)acrylic acid, andvinyl acetate. Vinyl chloride is suitably used. As the vinyl monomer, avinyl monomer that can be copolymerized with vinyl chloride may be usedtogether with vinyl chloride. Examples of the vinyl monomer that can becopolymerized with vinyl chloride include vinyl halides or vinylidenehalides such as vinyl bromide and vinylidene chloride; α-olefins such asethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene,1-nonene, 1-decene, 1-undecene, 1-dodecene, 1-tridecene, and1-tetradecene, acrylic acid; acrylic acid esters such as methylacrylate, ethyl acrylate, and butyl acrylate; vinyl esters such as vinylacetate and vinyl propionate; vinyl ethers such as lauryl vinyl etherand isobutyl vinyl ether; and aromatic vinyl such as styrene. The vinylmonomers that can be copolymerized with vinyl chloride may be usedsingly or may be used in combination of two or more of them.

As described above, the vinyl polymer to be produced is preferably avinyl chloride homopolymer using vinyl chloride alone as the vinylmonomer or a copolymer using vinyl chloride and the vinyl monomer thatcan be copolymerized with vinyl chloride as the vinyl monomers. In thecase of the copolymer, usually vinyl chloride is used in an amount of50% by mass or more in the vinyl monomers. In other words, in the methodfor producing the vinyl polymer according to the embodiment, thepolymerization step is preferably a step of polymerizing vinyl chlorideas the vinyl monomer to produce the vinyl chloride polymer (morespecifically, the vinyl chloride homopolymer) as the vinyl polymer.Alternatively, the polymerization step is also preferably a step ofpolymerizing vinyl chloride and the vinyl monomer that can becopolymerized with vinyl chloride to provide the vinyl chloride polymeras the vinyl polymer.

The polymerization step is carried out by, for example, the suspensionpolymerization. The polymerization conditions are not particularlylimited. For example, the vinyl monomer, the composition including themicrocapsule, the suspension agent, and the aqueous medium are chargedin the polymerization container and thereafter a temperature of thecontent in the polymerization container is raised while the content isbeing stirred to carry out the polymerization reaction. Specifically,the polymerization reaction is carried out at 20° C. to 80° C. for 1hour to 20 hours.

Composition Including Microcapsule

Here, the composition including the microcapsule used for the method forproducing the vinyl polymer according to the embodiment will bedescribed. As described above, the microcapsule included in thecomposition has the core/shell structure, in which the shell includesthe water-soluble polymer and the core includes the organic peroxide. Inthe microcapsule, the organic peroxide is encapsulated. In other words,the microcapsule is a coated particle-like substance having aparticle-like substance including the organic peroxide and the coatedlayer including the water-soluble polymer attached to the surface of theparticle-like substance. The formation of the core/shell structure canbe confirmed by the solubility of the microcapsule to ethylenedichloride (EDC) described in Examples below. The microcapsule isdispersed in, for example, an aqueous medium and forms a compositiontogether with the aqueous medium.

The water-soluble polymer included in the shell is preferably at leastone water-soluble polymer selected from the group consisting ofpolyvinyl alcohol, cellulose derivatives, gelatin, poly(meth)acrylicacid derivatives, polyvinylpyrrolidone, and polyethylene oxide. Thewater-soluble polymers may be used singly or may be used in combinationof two or more of them.

Polyvinyl alcohol is usually produced by saponifying a vinyl esterpolymer using a known method.

A vinyl ester monomer is not particularly limited and examples of thevinyl ester monomer may include fatty acid vinyl esters such as vinylacetate, vinyl formate, vinyl propionate, vinyl caprylate, and vinylversatate. These monomers may be used singly or in combination of two ormore of them.

At the time of polymerizing the vinyl ester monomer, the vinyl estermonomer may be copolymerized with other monomers. The other monomersthat can be used are not particularly limited. Examples of the othermonomers include α-olefins, acrylic acid and the salts thereof, acrylicacid esters, methacrylic acid and the salts thereof, methacrylic acidesters, acrylamide, acrylamide derivatives, methacrylamide,methacrylamide derivatives, vinyl ethers, nitriles, vinyl halides,vinylidene halides, allyl compounds, unsaturated dicarboxylic acid andthe salts thereof or the esters thereof, olefin sulfonic acids and thesalts thereof, vinyl silyl compounds, and fatty acid alkyl esters. Theseother monomers may be used singly or in combination of two or more ofthem.

At the time of the polymerization of the vinyl ester polymer, a chaintransfer agent may coexist for the purpose of, for example, adjustingthe degree of polymerization of the vinyl ester polymer to be obtained.The chain transfer agent is not particularly limited. Examples of thechain transfer agent include aldehydes such as acetaldehyde,propionaldehyde, butyraldehyde, and benzaldehyde; ketones such asacetone, methyl ethyl ketone, hexanone, and cyclohexanone; mercaptanssuch as 2-hydroxyethanethiol and dodecyl mercaptan; and organic halidessuch as carbon tetrachloride, carbon tetrabromide, dichloromethane,dibromomethane, trichloroethylene, and perchlorethylene. These chaintransfer agents may be used singly or in combination of two or more ofthem.

The polyvinyl alcohol may be polyvinyl alcohol provided by modifyingafter production of polyvinyl alcohol by the methods of acetoaceticesterification, acetalization, urethaneization, etherification,grafting, phosphate esterification, and oxyalkyleneation of polyvinylalcohol, that is, modified polyvinyl alcohol.

Examples of the cellulose derivatives include methylcellulose,ethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose,hydroxymethylpropylcellulose, and carboxymethylcellulose.

Examples of the poly(meth)acrylic acid derivatives include polyacrylicacid salts, polyacrylamide, and polyacrylic acid esters. Examples of thepolyacrylic acid salts include salts formed of a polyacrylic acid and amonovalent cation. Examples of the monovalent cation include Li⁺, Na⁺,K⁺, and NH₄ ⁺. Examples of the polyacrylic acid esters includepolyacrylic acid alkyl esters. The alkyl group in the polyacrylic acidalkyl esters is preferably an alkyl group having a carbon atom number of1 to 5 and more preferably an alkyl group having a carbon atom number of1 to 3.

Of these polymers, partially saponified polyvinyl alcohol is suitablyused as the water-soluble polymer because the fish eyes in the producedvinyl polymer can be more reduced.

The partially saponified polyvinyl alcohol preferably has a degree ofsaponification of 80% by mole or more and 99.5% by mole or less. Thedegree of saponification can be determined in accordance with the degreeof saponification measurement method of polyvinyl alcohol prescribed inJIS K 6726. A degree of saponification of less than 80% by mole maycause dissolution of the shell with the aqueous medium before thepolymerization initiator is uniformly dispersed in the polymerizationreactor. This may cause nonuniform concentration distribution of thepolymerization initiator and thus the fish eyes may be increased in theproduced vinyl polymer. On the other hand, a degree of saponification ofmore than 99.5% by mole may be unfavorable from an economic standpointdue to requiring much energy for heating and dissolution.

The partially saponified polyvinyl alcohol preferably has an averagedegree of polymerization of 1,500 or more and 3,500 or less. The averagedegree of polymerization can be determined in accordance with theaverage degree of polymerization measurement method of polyvinyl alcoholprescribed in JIS K 6726. A degree of polymerization of less than 1,500may cause dissolution of the shell with the aqueous medium before thepolymerization initiator is uniformly dispersed in the polymerizationreactor. This may cause nonuniform concentration distribution of thepolymerization initiator and thus the fish eyes may be increased in theproduced vinyl polymer. In particular, in the case of high temperaturewater charge polymerization method, this tendency becomes remarkable andsignificant increase in fish eyes may occur. On the other hand, a degreeof polymerization of more than 3,500 may result in requiring excessivetime for dissolving the shell and thus also requiring excessive time forpenetrating the polymerization initiator into the oil droplet of thevinyl monomer. Therefore, although the fish eyes can be reduced,polymerization time becomes longer and thus productivity maydeteriorate, which is unfavorable.

The organic peroxide included in the core preferably has a 10-hourhalf-life temperature in benzene at a concentration of 0.1 mol/L of 70°C. or less and more preferably 30° C. or more and 70° C. or less. A10-hour half-life temperature of more than 70° C. requires anexcessively large amount of the organic peroxide and thus may result indeteriorating the initial colorability, extraction resistance, and thelike of the produced vinyl polymer. On the other hand, a 10-hourhalf-life temperature of less than 30° C. may cause the activity of theorganic peroxide serving as the polymerization initiator to be difficultto retain. In the present specification, the 10-hour half-lifetemperature is also called T10-HDT.

Specific examples of the organic peroxide include a diacyl peroxidecompound, a peroxydicarbonate compound, and a peroxyester compound,which have the 10-hour half-life temperature within the above range. Theorganic peroxides may be used singly or may be used in combination oftwo or more of them.

Examples of the diacyl peroxide compound include a compound representedby the following general formula (1).

In the formula (1), two R¹s may be the same as or different from eachother and are substituted or unsubstituted alkyl groups having a carbonatom number of 1 to 12. The alkyl groups may be linear, branched, orcyclic. Examples of the alkyl groups include n-alkyl groups such as amethyl group, an ethyl group, a n-propyl group, a n-butyl group, an-pentyl group, a n-hexyl group, a n-heptyl group, a n-octyl group, an-nonyl group, a n-decyl group, a n-undecyl group, and a n-dodecylgroup; sec-alkyl groups; tert-alky groups such as a tert-butyl group, atert-pentyl group, a tert-hexyl group, a tert-nonyl group, and atert-decyl group; isoalkyl groups such as an isopropyl group, anisobutyl group, an isopentyl group, an isoheptyl group, and an isooctylgroup; cycloalkyl groups such as a 1-cyclohexyl-1-methylethyl group; anda 2,4,4-trimethylpentyl group.

As the diacyl peroxide compound, more specifically dilauroyl peroxide(T10-HDT=62° C.), di(3,5,5-trimethylhexanoyl)peroxide (T10-HDT=59° C.),diisobutyl peroxide (T10-HDT=33° C.), disuccinic acid peroxide(T10-HDT=65° C.), and the like are suitably used.

Examples of the peroxydicarbonate compound include a compoundrepresented by the following general formula (2).

In the formula (2), two R²s may be the same as or different from eachother and are substituted or unsubstituted alkyl groups having a carbonatom number of 1 to 10. The alkyl groups may be linear, branched, orcyclic. Examples of the alkyl groups include n-alkyl groups such as amethyl group, an ethyl group, a n-propyl group, a n-butyl group, an-pentyl group, a n-hexyl group, a n-heptyl group, a n-octyl group, an-nonyl group, and a n-decyl group; sec-alkyl groups; tert-alky groupssuch as a tert-butyl group, a tert-pentyl group, a tert-hexyl group, atert-nonyl group, and a tert-decyl group; isoalkyl groups such as anisopropyl group, an isobutyl group, an isopentyl group, an isoheptylgroup, and an isooctyl group; cycloalkyl groups such as a1-cyclohexyl-1-methylethyl group; and a 2,4,4-trimethylpentyl group.

As the peroxydicarbonate compound, more specificallydi-(2-ethylhexyl)peroxydicarbonate (T10-HDT=44° C.), di-n-propylperoxydicarbonate (T10-HDT=40° C.), diisopropyl peroxydicarbonate(T10-HDT=41° C.), di-(4-t-butylcyclohexyl)peroxydicarbonate (T10-HDT=41°C.), di-sec-butyl peroxydicarbonate (T10-HDT=41° C.), and the like aresuitably used.

Examples of the peroxyester compound include a compound represented bythe following general formula (3).

In the formula (3), two R^(a)s may be the same as or different from eachother and are substituted or unsubstituted alkyl groups having a carbonatom number of 1 to 10 or aralkyl groups having a carbon atom number of7 to 10. The alkyl groups may be linear, branched, or cyclic. Examplesof the alkyl groups include n-alkyl groups such as a methyl group, anethyl group, a n-propyl group, a n-butyl group, a n-pentyl group, an-hexyl group, a n-heptyl group, a n-octyl group, a n-nonyl group, and an-decyl group; sec-alkyl groups; tert-alky groups such as a tert-butylgroup, a tert-pentyl group, a tert-hexyl group, a tert-nonyl group, anda tert-decyl group; isoalkyl groups such as an isopropyl group, anisobutyl group, an isopentyl group, an isoheptyl group, and an isooctylgroup; cycloalkyl groups such as a 1-cyclohexyl-1-methylethyl group; a2,4,4-trimethylpentyl group; and examples of the aralkyl groups includegroups such as a 2-phenylpropan-2-yl group.

As the peroxyester compound, more specifically t-butylperoxyneodecanoate (T10-HDT=46° C.), t-hexyl peroxyneodecanoate(T10-HDT=45° C.), t-butyl peroxypivalate (T10-HDT=54.6° C.), t-hexylperoxypivalate (T10-HDT=53° C.), α-cumyl peroxyneodecanoate (T10-HDT=37°C.), t-butyl peroxyneoheptanoate (T10-HDT=51° C.), t-amylperoxyneodecanoate (T10-HDT=43° C.), 1,1,3,3-tetramethylbutylperoxyneodecanoate (T10-HDT=41° C.), 1,1,3,3-tetramethylbutylperoxypivalate (T10-HDT=48° C.), and the like are suitably used.

The 10-hour half-life temperature (T10-HDT) can be determined asfollows. A benzene solution in which the organic peroxide concentrationis 0.1 mol/L is prepared. The solution is sealed in a glass tube purgedwith nitrogen and the tube was immersed into a constant temperature bathadjusted to the predetermined temperature to thermally decompose theorganic peroxide. The change in the concentration of the organicperoxide relative to time is measured. In the reaction conditions, thedecomposition reaction of the organic peroxide can be approximatelytreated as a first-order reaction and thus the following formulas (4)and (5) are true.dx/dt=k(a−x)  (4)ln[a/(a−x)]32 kt  (5)

In the two formulas (4) and (5), x represents the concentration of thedecomposed organic peroxide, a represents the initial concentration ofthe organic peroxide, k represents a decomposition rate constant, and trepresents time. The half-life refers to a time required to decrease theorganic peroxide concentration to a half of the initial concentration bydecomposition. Therefore, the half-life is represented by t_(1/2) anda/2 is substituted for x in the formula (5) to obtain the followingrelational formula.kt _(1/2) =ln2  (6)

From the concentration change of the organic peroxide measured above,the relation between the time t and ln[a/(a−x)] is plotted. The gradientof the obtained straight line is determined to be k and thus thehalf-life t_(1/2) is determined at the temperature from the formula (6).Therefore, the 10-hour half-life temperature can be determined as atemperature at which t_(1/2) of a certain organic peroxide is 10 hours.

The particle diameter of the microcapsule is not particularly limited.The median diameter (D50) of the microcapsule is preferably 15 μm orless and more preferably 0.5 μm or more and 15 μm or less. The mediandiameter (D50) within the above range allows the storage stability ofthe microcapsule in which the organic peroxide in the aqueous medium isencapsulated to be more secured.

As described above, the above-described microcapsule is, for example,dispersed in the aqueous medium to form the composition together withthe aqueous medium. The content of the organic peroxide in thecomposition (aqueous liquid) is usually 10% by mass or more and 70% bymass or less and preferably 15% by mass or more and 65% by mass or less,and more preferably 30% by mass or more and 60% by mass or less. Acontent of the organic peroxide of less than 10% by mass may result inhigh transport cost and thus may be unfavorable from an economicstandpoint.

Examples of the aqueous medium include water such as clean water,ion-exchanged water, distilled water, and ultrapure water and mixedmedia of water with a water-soluble organic solvent. Examples of thewater-soluble organic solvent include alcohols such as methanol,ethanol, n-propanol, isopropanol (2-propanol), ethylene glycol, anddiethylene glycol. In the case where the aqueous medium is the mixedmedium, the content of the water-soluble organic solvent in the aqueousmedium is preferably more than 0% by mass and 50% by mass or less.

The above-described microcapsule is preferably prepared by an emulsionmethod. Specifically, the microcapsule can be prepared by rotationallymixing the water-soluble polymer (for example, the partially saponifiedpolyvinyl alcohol), the organic peroxide, and the aqueous medium. Here,the rotation mixing is preferably carried out at high speed rotation andmay be carried out while the number of rotation is appropriately beingadjusted. The number of rotation is preferably 1,000 rpm or more and3,000 rpm or less. The mixing can be suitably emulsified in −30° C. ormore and 50° C. or less and preferably −20° C. or more and 30° C. orless for 30 seconds or more and 120 minutes or less. Consequently, thecomposition (the aqueous liquid) in which the microcapsule is dispersedin the aqueous medium is obtained.

An apparatus to be used may be a well-known apparatus. Examples of theusable apparatus include a mechanical rotation-type stirrer, a highspeed rotation shear-type stirrer, a colloid mill, a pearl mill, ahomogenizer, a pressurized homogenizer, an ultrasonic homogenizer, ahomomixer, and a microfluidizer.

In the mixing, the aqueous medium is desirably used in an amount of 30parts by mass or more and 180 parts by mass or less and more preferablyin an amount of 20 parts by mass or more and 150 parts by mass or lessrelative to the 100 parts by mass of the organic peroxide.

In the mixing, the water-soluble polymer (for example, the partiallysaponified polyvinyl alcohol) is preferably used in an amount of 0.001part by mass or more and 30 parts by mass or less and more preferablyused in an amount of 0.01 part by mass or more and 25 parts by mass orless relative to 100 parts by mass of the organic peroxide.

In the mixing, the organic peroxide may be used by previouslyemulsifying with an isoparaffin solvent in order to dilute or dissolvethe organic peroxide. In the mixing, a surfactant may be further added,if necessary.

The above-described microcapsule may be prepared by known microcapsuleformation methods other than the emulsion method. Examples of the knownmicrocapsule formation methods other than the emulsion method include acoacervation method, a spray drying method, a drying method in liquid,and an in-situ method.

In the polymerization step, the composition including the microcapsuleencapsulating the organic peroxide is preferably used in an amount ofthe microcapsule included in the composition of 0.01 part by mass to 0.5part by mass or less relative to 100 parts by mass of the vinyl monomer.

As the suspension agent charged into the polymerization container,specifically, the water-soluble polymer is used. Examples of thewater-soluble polymer include water-soluble cellulose ethers such asmethylcellulose, hydroxyethylcellulose, hydroxypropylcellulose, andhydroxypropylmethylcellulose; water-soluble or oil-soluble partiallysaponified polyvinyl alcohols; (meth)acrylic acid polymers; and gelatin.The suspension agents may be used singly or may be used in combinationof two or more of them. The suspension agent is usually used in anamount of 0.02 part by mass or more and 5.0 parts by mass or less andpreferably in an amount of 0.04 part by mass or more and 1.5 parts bymass or less relative to 100 parts by mass of the vinyl monomer.

Examples of the aqueous medium charged into the polymerization containerinclude water such as clean water, ion-exchanged water, distilled water,and ultrapure water and mixed media of water with a water-solubleorganic solvent. Examples of the water-soluble organic solvent includealcohols such as methanol, ethanol, n-propanol, isopropanol(2-propanol), ethylene glycol, and diethylene glycol. In the case wherethe aqueous medium is the mixed medium, the content of the water-solubleorganic solvent in the aqueous medium is preferably more than 0% by massand 50% by mass or less. The aqueous medium is usually used in an amountof 90 parts by mass or more and 250 parts by mass or less and preferablyin an amount of 100 parts by mass or more and 200 parts by mass or lessrelative to 100 parts by mass of the vinyl monomer.

At the time of the polymerization, other additives may be added into thepolymerization container, if necessary. Examples of the additivesinclude oil-soluble polymerization initiators except the organicperoxides; adjusting agents for the degree of polymerization such asacetaldehyde, butyraldehyde, trichlorethylene, perchlorethylene, andmercaptans; and polymerization inhibitors such as phenol compounds,sulfur compounds, and N-oxide compounds. In addition, for example, pHadjusters, scale prevention agents, or crosslinking agent may be used asthe additives. The additives may be used singly or may be used incombination of two or more of them.

The composition including the microcapsule may be collectively added ormay be intermittently or continuously added to the polymerizationcontainer depending on the purpose of use. Each of the vinyl monomer,the suspension agent, and the aqueous medium may be charged on the wayduring the polymerization.

In the method for producing the vinyl polymer described above, thepolymerization step may be carried out by using vinyl chloride in anamount of less than 50% by mass as the vinyl monomer. The polymerizationstep may be carried out not using vinyl chloride but using the vinylmonomer alone that can be copolymerized with vinyl chloride.

In the method for producing the vinyl polymer, the polymerization stepmay be carried out by a polymerization type except the suspensionpolymerization. Specifically, the polymerization type is notparticularly limited as long as the radical polymerization reaction ofthe vinyl monomer can be carried out. Examples of the polymerizationtype may include emulsion polymerization, bulk polymerization, and finesuspension polymerization.

The present invention is not limited by the embodiment. Productsconstituted by appropriately combining the constituents described aboveare included in the present invention. Further effects and modificationexamples can be easily evolved by those skilled in the art. Thus, thewider aspect of the present invention is not limited by the embodimentand various modifications are possible.

EXAMPLES

Hereinafter, the embodiment will be described in detail based onExamples carried out in order to clarify the effect of the embodiment.The embodiment is not limited at all by Examples and ComparativeExamples described below.

Example 1

(1) Production of Aqueous Liquid Including Microcapsule

Into a 500 ml four-necked flask equipped with a common stirring deviceand a thermometer, 15 parts by mass of water, 10 parts by mass of theaqueous solution of partially saponified polyvinyl alcohol(concentration 10% by mass) having a degree of saponification of 88% bymole and an average degree of polymerization of 1,800, 17 parts by massof ethanol, and 3 parts by mass of a surfactant (sorbitan monooleate)were charged and dissolved, and thereafter the temperature inside theflask was adjusted to 5° C. to 10° C. To this solution, 55 parts by massof di-(2-ethylhexyl)peroxydicarbonate was added dropwise as the organicperoxide and the resultant mixture was vigorously stirred. The mixturewas further stirred for 30 minutes to give an aqueous liquid (amicrocapsule composition liquid) including the microcapsule into whichdi-(2-ethylhexyl)peroxydicarbonate was encapsulated. In Table 1, themedian diameter (D50) of the obtained microcapsule measured with a laserdiffraction type particle size distribution measuring apparatus islisted.

(2) Evaluation of Solubility to Ethylene Eichloride (EDC)

The solubility of the microcapsule to ethylene dichloride (EDC) wasevaluated by the following method. Into a 500 ml beaker, 150 parts bymass of water, 50 parts by mass of the aqueous liquid including themicrocapsule, and 100 parts by mass of EDC were charged and theresultant mixture was stirred using a common stirring device at aninternal temperature of 40° C. for 5 minutes. Thereafter, the stirredmixture was allowed to stand. A state when the EDC phase and the waterphase were separated was observed and the evaluated in accordance withthe following criteria. The result is listed in Table 1. o: A statewhere almost no microcapsule is dissolved in the EDC phase Δ: A statewhere less than half of the total amount of the microcapsule isdissolved in the EDC phase ×: A state where a half or more of the totalamount of the microcapsule is dissolved in the EDC phase

In order to reduce fish eyes in the produced vinyl polymer, formation ofthe microcapsule having the core/shell structure is required. In otherwords, it is required that the microcapsule is not immediately dissolvedin the vinyl polymer but is dispersed in the aqueous medium for acertain period after the microcapsule is charged into the polymerizationreactor. Therefore, using the suspension polymerization method of vinylchloride as a model and EDC as a pseudo substance of vinyl chloride, thesolubility of the microcapsule to EDC was evaluated. An excellentevaluation result allows formation of the microcapsule having thecore/shell structure to be confirmed.

(3) Production of Vinyl Chloride Polymer

Into a stainless-steel polymerization reactor having an interior contentof 2 m³, 876 kg of deionized water, 182.5 g of hydroxypropylmethylcellulose, 182.5 g of partially saponified polyvinyl alcoholhaving a degree of saponification of 80.5% by mole and an average degreeof polymerization of 2,500, and 65 g of partially saponified polyvinylalcohol having a degree of saponification of 48% by mole and an averagedegree of polymerization of 230 were charged. The inside of thepolymerization reactor was degassed to an inner pressure of 8 kPa(absolute pressure) and thereafter 730 kg of the vinyl chloride monomerwas charged. With stirring, the aqueous liquid including themicrocapsule obtained in (1) encapsulating the polymerization initiatorwas charged in a mass of 400 g in terms of the pure organic peroxide andthe temperature rising was simultaneously started by flowing warm waterthrough the jacket. At the stage where the temperature in thepolymerization reactor reached 57.0° C., this temperature was retainedand the polymerization was continued.

At the time when a polymerization conversion ratio reached 88%, 186 g of35% by mass aqueous dispersion liquid of triethyleneglycol-bis[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] was addedinto the polymerization reactor and subsequently the unreacted monomerwas recovered. The polymer slurry was dehydrated and dried to produce avinyl chloride polymer.

The apparent specific gravity, the average particle diameter, theplasticizer absorption amount, and the number of fish eyes of theobtained polymer were measured in accordance with the following methods.The results are listed in Table 1.

—Apparent Density—

The apparent density of the sample polymer was measured in accordancewith JIS K 7365.

—Average Particle Diameter—

Sieves having a nominal dimension of 300 μm, 250 μm, 180 μm, 150 μm, 106μm, and 75 μm in the testing sieves prescribed in JIS Z 8801 wereattached to a low-tap type sieve shaker. Onto the top sieve, 100 g ofthe sample polymer was gently poured. After 10-minute shake, the mass ofthe sample polymer remaining on each of the sieves was measured andpercentages (A to F) to the total mass (100 g) were determined. A:Remaining ratio (%) on the sieve having a nominal dimension of 250 μm B:Remaining ratio (%) on the sieve having a nominal dimension of 180 μm C:Remaining ratio (%) on the sieve having a nominal dimension of 150 μm D:Remaining ratio (%) on the sieve having a nominal dimension of 106 μm E:Remaining ratio (%) on the sieve having a nominal dimension of 75 μm F:Passing ratio (%) through the sieve having a nominal dimension of 75 μm

The average particle diameter was determined by substituting thedetermined remaining ratios and the passing ratio of each of the sievesin the following formula.Average particle diameter(μm)={(A×300)+(B×215)+(C×165)+(D×128)+(E×90)+(F×60)}×(1/100)

—Plasticizer Absorption Amount—

The plasticizer absorption amount (%) of the sample polymer was measuredin accordance with JIS K 7386.

—Number of Fish Eyes—

One hundred parts by mass of the sample polymer, 50 parts by mass ofbis(2-ethylhexyl)phthalate (DOP), 2.0 parts by mass of Ba/Zn stabilizer,5.0 parts by mass of epoxidized soybean oil, 0.1 part by mass of carbonblack, and 0.5 part by mass of titanium dioxide were mixed to produce acompound. With a roll mill, 50 g of this compound was kneaded at 145° C.for 5 minutes to be partially taken as a sheet having a thickness of 0.3mm. The number of fish eyes was determined by counting the number ofclear particles in 100 cm² of this sheet.

Example 2

The same procedure as the procedure in Example 1 was carried out exceptthat the partially saponified polyvinyl alcohol used in the productionof the aqueous liquid including the microcapsule was replaced withpartially saponified polyvinyl alcohol having a degree of saponificationof 88% by mole and an average degree of polymerization of 3,300. Theresults are listed in Table 1.

Example 3

The same procedure as the procedure in Example 1 was carried out exceptthat the partially saponified polyvinyl alcohol used in the productionof the aqueous liquid including the microcapsule was replaced withpartially saponified polyvinyl alcohol having a degree of saponificationof 82% by mole and an average degree of polymerization of 2,400. Theresults are listed in Table 1.

Example 4

The same procedure as the procedure in Example 1 was carried out exceptthat the partially saponified polyvinyl alcohol used in the productionof the aqueous liquid including the microcapsule was replaced withpartially saponified polyvinyl alcohol having a degree of saponificationof 98% by mole and an average degree of polymerization of 1,700. Theresults are listed in Table 1.

Example 5

The same procedure as the procedure in Example 1 was carried out exceptthat in the production of the microcapsule composition liquid, thematerials were replaced with 40 parts by mass of water, 5 parts by massof an aqueous solution (concentration 10% by mass) of the partiallysaponified polyvinyl alcohol, and 35 parts by mass ofdi-(2-ethylhexyl)peroxydicarbonate. The results are listed in Table 1.

Example 6

The same procedure as the procedure in Example 1 was carried out exceptthat the partially saponified polyvinyl alcohol used in the productionof the aqueous liquid including the microcapsule was replaced withgelatin. The results are listed in Table 1.

Example 7

The same procedure as the procedure in Example 1 was carried out exceptthat the organic peroxide used in the production of the aqueous liquidincluding the microcapsule was replaced with t-butyl peroxyneodecanoate.The results are listed in Table 1.

Comparative Example 1

The same procedure as the procedure in Example 1 was carried out exceptthat an isoparaffin solution of di-(2-ethylhexyl)peroxydicarbonatehaving a concentration of 70% was used instead of the microcapsulecomposition liquid. The results are listed in Table 1. In this case, thefish eyes of the obtained vinyl chloride polymer increased and thus thequality of the formed product of the vinyl chloride polymerdeteriorated.

Comparative Example 2

The same procedure as the procedure in Example 1 was carried out exceptthat the partially saponified polyvinyl alcohol was not used in theproduction of the microcapsule composition liquid. The results arelisted in Table 1. In this case, the microcapsule was not formed but anagglomerate having a median diameter of 200 μm was formed.

TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5 AqueousPartially Degree of % by mole 88 88 82 98 88 liquid saponifiedsaponification including polyvinyl Average degree of 1,800 3,300 2,4001,700 1,800 microcapsule alcohol polymerization Organic peroxide *1 A AA A A Median diameter μm 4 6 2 8 3 Solubility to EDC — ◯ ◯ ◯ ◯ ◯ VinylApparent specific gravity g/ml 0.570 0.572 0.568 0.577 0.574 chlorideAverage particle diameter μm 143 138 156 148 141 polymer Plasticizerabsorption amount % 22.6 22.3 22.7 22.1 22.0 Number of fish eyes Counts1 3 0 3 5 Comparative Comparative Example 6 Example 7 Example 1 Example2 Aqueous Partially Degree of % by mole Gelatin 88 — — liquid saponifiedsaponification including polyvinyl Average degree of 1,800 — —microcapsule alcohol polymerization Organic peroxide *1 A B A A Mediandiameter μm 12 3 — >200 Solubility to EDC — ◯ ◯ X X Vinyl Apparentspecific gravity g/ml 0.565 0.569 0.573 — chloride Average particlediameter μm 162 147 152 — polymer Plasticizer absorption amount % 23.022.8 22.5 — Number of fish eyes Counts 2 0 82 — *1 A =di-(2-ethylhexyl)peroxydicarbonate, B = t-butyl peroxyneodecanoate

From the results listed in Table 1, it has been found that, with theabove-described microcapsule, the vinyl polymer having the extremelysmall number of fish eyes can be obtained in the production of thepolymer particularly using the vinyl chloride monomer or the vinylchloride monomer and the monomer that can be copolymerized with thevinyl chloride monomer among the production of the vinyl polymers towhich improved productivity is required. In addition, it has been foundthat the polymerization stability and the basic properties of the vinylpolymer can be retained.

According to the present embodiment, a method for producing a vinylpolymer that can reduce fish eyes in the produced vinyl polymer can beprovided.

Although the invention has been described with respect to specificembodiments for a complete and clear disclosure, the appended claims arenot to be thus limited but are to be construed as embodying allmodifications and alternative constructions that may occur to oneskilled in the art that fairly fall within the basic teaching herein setforth.

What is claimed is:
 1. A method for producing a vinyl polymer, themethod comprising: a polymerization step of using a composition thatincludes a microcapsule and polymerizing a vinyl monomer by radicalreaction to produce a vinyl polymer, wherein the microcapsule has acore/shell structure, the shell includes a water-soluble polymer and thecore includes an organic peroxide, and said microcapsule has a mediandiameter (D50) of 15 μm or less.
 2. The method for producing the vinylpolymer according to claim 1, wherein the water-soluble polymer is atleast one water-soluble polymer selected from the group consisting ofpolyvinyl alcohol, a cellulose derivative, gelatin, a poly(meth)acrylicacid derivative, polyvinylpyrrolidone, and polyethylene oxide.
 3. Themethod for producing the vinyl polymer according to claim 2, wherein thepolyvinyl alcohol is partially saponified polyvinyl alcohol having adegree of saponification of 80% by mole or more and 99.5% by mole orless and an average degree of polymerization of 1,500 or more and 3,500or less.
 4. The method for producing the vinyl polymer according toclaim 1, wherein the organic peroxide has a 10-hour half-lifetemperature in benzene at a concentration of 0.1 mol/L of 70° C. orless.
 5. The method for producing the vinyl polymer according to claim1, wherein the polymerization step is a step of polymerizing vinylchloride as the vinyl monomer to produce a vinyl chloride polymer as thevinyl polymer.
 6. The method for producing the vinyl polymer accordingto claim 1, wherein the water-soluble polymer is at least onewater-soluble polymer selected from the group consisting of polyvinylalcohol, a cellulose derivative, a poly(meth)acrylic acid derivative,polyvinylpyrrolidone, and polyethylene oxide.